VI User Manual - 第243页

Tools library Vision 2007 4.10 User Manua l Rev 01 7 - 81 4. In Import / Export config u- ration file ( E ) section, you can choose to impo rt or export a configuration file (.cfg file). 5. Press Test ( F ) button to lau…

Tools library

7 - 80 Vision 2007 4.10 User Manual Rev 01

7.13 Bar code CVB model

7.13.1 Model description tab

1. On the Model description tab, in the Edit a model window, click on the button. The

.bmp file name to add in picture list window appears.

2. Select the image on which load the treatment.

3. Click on Edit area button to define the component size.

4. Choose the treatment operation: Barcode CVB. A new Bar code tab appears behind the

Model description tab.

7.13.2 Bar code tab

1. In Camera (A) section, select

the camera used to read the bar

code. The external camera take

picture during the board loading.

2. In Bar code color (B) section,

select the bar code type among

the 2 available:

 Black code on a white back-

ground,

 White code on a black back-

ground.

3. In Bar code types (C) section,

select the bar code coding type to

read.

The

All (D) button is used to se-

lect or deselect all coding type.

If you have chosen an ex-

ternal camera, the search

area is not use, the

software take care of the

entire image.

The CVB bar code reader is able to read several different bar code coding type. If

you do not know the coding type select all the type but it is time consuming. It is

better to select only the one you use.

Tools library

Vision 2007 4.10 User Manual Rev 01 7 - 81

4. In Import / Export configu-

ration file

(E) section, you can

choose to import or export a

configuration file (.cfg file).

5. Press Test (F) button to

lauch the Data Matrix reading test. The standard result

(score, XY position, theta, ...)

and the

decoded character string are displayed.

You can also see the result in the COGNEX con-

sole.

The .cfg file contain

bar code coding

type parameters. It

is an ASCII file.

Bar code CVB model

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7.14 Blob

7.14.1 Blob tool definition

The Blob tool detects random shapes based on the gray levels in the image. It identifies

groups of pixels that fall into a user defined gray scale range. Several parameters allow

shape-based filtering.

The Blob tool is used to find contrasted objects, when the object shape is not known precisely.

It can find pin tips for backplane or connector inspection, polarity marks, solder defects as pin-

holes, missing or excess solder, or various PCB pollution... It returns presence, X, Y and The-

ta position of the biggest found shape. Blob runs in several steps:

7.14.1.1 Segmentation

This step determines which pixels are object pixels or background pixels. Two types

of segmentations are available:

Fixed thresholding

The division between object

and background pixels is deter-

mined by a gray level value

Relative thresholding

The threshold is computed ac-

cording to the values of all the

pixels in the search area. 2 “tail”

parameters represent the per-

centage of noise-level pixels

that are excluded from the

threshold calculation. The

threshold is a percentage of the

gray levels range without the

tails.

7.14.1.2 Masking

The Blob can apply a mask that will exclude some portions of the segmented image.

The mask is a binary bitmap image. The center of this bitmap is realigned with the

center of the tool’s search area. Pixels of the segmented image covered with the

mask’s black pixels won’t be analyzed.

7.14.1.3 Blob analysis

The tool finds groups of pixels in the segmented and masked image. It returns vari-

ous shape parameters that tend to describe the shape features: Area, Acircularity,

Elongation, Angle.

Area

The area is the number of pixels included in the shape, multiplied by the area of a

single pixel (X pixel size * Y pixel size).

From now on, the blob search area is adapted to pad with angles: a mask is applied

to the search area to simulate the search area rotation. The sidewalk has then to be

set (set to 0 by default by the customers to avoid false defects).

0255Gray levels

Threshold

Background Object

0255Gra

levels

Low tail High tail

Threshold

Background Object